you must understand removing wood to save weight, makes the plane more fragile and is a lot of work. Get a scale and see how much balsa it takes to weigh one ounce. How much weight do you want to save?

I would build up the ailerons instead of the solid ones provided. Also check the density of the supplied balsa and replace any heavy pieces. Try to remove 10% of the wood from every piece. Never add any plywood, it's just too heavy.

You'll find the biggest payoff comes from light weight equipment. Use the smallest possible fuel tank and battery. Just one elevator servo should be enough for this plane. Light weight wheels are a must. Most of all, check the CG as soon as possible to avoid adding weight.

A YS90 is plenty for all the pattern stuff.

Tom